In a bowl, mix the plum halves with the sugar, 1 teaspoon cinnamon, lemon juice and marsala. Then spread the plums in a casserole or quiche dish (28 cm) greased with butter.
Preheat the oven to 180 ° C.
In a second bowl mix the oatmeal, brown sugar, 1/2 teaspoon cinnamon and flour. Now you knead in the softened butter until everything has mixed and scatter the mixture crumbly over the plums.
Bake the plum crumble for approx. 40 minutes until golden brown. If you like the crumbs a little more crispy and crisp brown, you can set the grill function on the oven for a short time until the desired brown is achieved.
Plum crumble tastes best when you serve it hot.
It goes well with whipped cream or vanilla ice cream.